Power control apparatus



POWER CONTRbL APPARATUS Filed Feb. 19, 1937 INVENTOR Jesse Malzsfen BY 6%, 0M r/ W? ATTORNEY mama May 21, 1940 UNITED STATES PATENT OFFICE 2,201,686 POWER CONTROL APPARATUS Application February 19, 1937. Serial No. 126,668

' 6 Claims. .(01. 20148) This invention relates to power control apparatus.

One of the objects of this invention is to pro-,

vide power control apparatus which is simple,

practical and thoroughly durable. Another object isto provide apparatus of the above character which maybe easily manufactured with a minimum labor and material cost, Another objecteis to provide apparatus of the above character which will operate accurately and reliably for long periods of time. Another object is to provide apparatus of the above character having a high current carrying capacity and ready adaptability to different conditions of use. An-

other object is to provide apparatus of the above character whose high current carrying capacity does not interfere with a minute regulation of resistance values in the circuit. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements and arrangements of parts as will be exemplified in the structure to be hereinafter described and the scope of the application of which will be 2 indicated in the following claims;

In the accompanying drawing in which is shown one of the various possible embodiments of this invention, 3a Figure 1 is a horizontal cross section of the power control apparatus showing the resistance element in place;

Figure 2 is a horizontal cross section of the apparatus with the resistance element removed; Figure 3 is a vertical sectional view of the apparatus taken along the line 3-4 of Figure 2;

and

Figure 4 is a perspective view of the apparatus as completely assembled. Similar reference characters refer to similar parts throughout the several views of the drawing.

As conducive to a clearer understanding of certain features of this invention, it might be pointed out that in power control apparatus it is often desirable to provide for a minute varia: tion in resistance values. In apparatus capable of achieving such minute and delicate control of resistance values, it is often desirable to utilize materials characterized by low critical temperatures; if the apparatus is subjected toappreciable current values, such materials may be seriously damaged. Fmthermore, in power control apparatus utilizing resistance strips, hot points may appear along the linear length of the resistance strip and obviously the current passing through the apparatusmust be so limited that these hot points" will not rise above the critical temperatures of the material from which the resistance strip and adjacent apparatus is made. 5 For these and other reasons, power control ap-' paratus now in use often has severe current carrying limitations making it unsuitable for a variety of purposes. One of the objects of this invention is to provide apparatus in which the 1 several difliculties hereinabovementioned as well as many others are successfully eliminated.

Referring now to Figures 1 and 3, there is provided a base generally indicated at it preferably circular in shape and formed from an 15 insulated material, desirably a-phenolic conden-- sation product. A series of ridges ll, l2, l3

and II extend upwardly from the plane surface of base it, thereby forming a border about the edge of the base. Ridges ll, l2, l3 and I are 2 spaced from each other toprovide slots l5, l6,

l1 and IS. A raised portion IQ of base It extends inwardly from the edge thereof and is bordered by side flanges 20 and 2| thereby forming a channel 22 for a purpose to be described hereinafter.

Referring more, particularly to Figure 3, a hole generally indicated at 23 is formed in the central portion of base Ill. The upper portion 24, of hole 23 is preferably hexagonal in shape (Figure 2) while the lower portion 25 thereof is round, thereby providing a series of shoulders 26 therein. A bushing generally indicated at 21 fits snugly within hole 23 having a hexagonal portion 28 resting within portion 24 of hole 23 and upon shoulders 26. BushingZl is provided with a central bore 29 and a threaded portion III for attachment purposes.

A shaft Si is rotatably mounted within bore 29 and has suitably secured thereto an arm 32 (Figure 3) carrying a'brush or contactor 33 con- 40 tacting a resistance strip generally indicated at '34 in amanner to be more fully described hereinafter. Consequently rotation ofshaft 3| moves armature brush 33 along resistance strip 34 to effect variation in resistance values as desired. Resting upon the top surface of base It and. preferably fitting snugly within ridges ll, l2, l3 and i4 is a flat metal plate generally indicated at 35. Asbest shown in Figure 2, plate 35 is substantially circular in shape having a central aperture 38 through which bushing 21 extends. The end portions 31 and 38 of plate 35 (Figure 2). are located adjacent the shoulders formed by upraised portion [9 of.the base. Plate 35 is desirably formed from a material having high heat conducting characteristics as, for example, copper.

As best shown in Figure 2, a portion 33 of plate 33 extends inwardly and thence downwardly in hole 23 so that it contacts bushing 21 (Figure 3). Ear portions 43, 4|, 42 and 43 of plate 35 extend outwardly through slots l5, i3, i1 and I3 respectively and thence down along the sides of the base. The extremitiesJlia, 4ia, 42a, and 43a of ear portions 45, 4|, 42 and 43 are bent over upon a metallic plate 44 resting upon the bottom of base 13 as will be seen from a consideration of Figures 3 and 4. Plate 44 (Figure 4) is substantially circular in shape and is formed to fit about the bottom of base I3; it is provided with an aperture 45 through which bushing 21 (Figure 3) extends.

It will now become clear that bushing 21, plate 35 and bottom plate '44 are interconnected in such a manner that heat developed in one portion thereof will be quickly distributed throughout these various interconnected parts. For example, heatdeveioping in one portion of plate 35 will be' rapidly transmitted throughout the entire plate; it will also be transmitted to bushing 21 by way of portion 39 (Figures 2 and 3) and to bottom plate 44 by way of ears 45, 4!, 42 and 43.

Resistance strip 34 is preferably formed from some dielectric composition and fits snugly upon plate 35 within ridges II, i2, i3 and 14 (Figure 1). The end portions of resistance strip 34, adjacent raised portion 19 of base ID, are provided with highly conductive coatings 4,3 and 41. A pair of rivets 48 and 49 (Figure 2) extend through strip 34, plate 35, base I0 and are headed over upon a pair of terminal projections 55 and 5| (Figure 4) As more clearly shown in Figure 2, holes 52 and 53 in plate 35 through which rivets 43 and 48 extend are larger than the rivets; thus plate 35 is insulated from these rivets. The heads 43a and 49a of rivets 45 and 48 rest firmly against conductive coatings 45 and 41 of strip 34 providing a sound electrical connection between the opposite ends of strip 34 and terminal projections and 5|.

A resistance coating 54 extends from conductlve coatings 46 and 41 about strip 34; such a coating may comprise --carbonaceous material suspended in a binder such as varnish. The

upper portion of strip 34, as shown in Figure 1, "is wider than the resistance coating 54 to provide a flat insulated portion 55 on strip 34. A pair of rivets 56 and 51 extend through strip 34, plate 35 and base It to hold this portion of the strip in flat engagement with plate 35.

It will now become clear that rivets '43, '43, 53 and 51 hold all portions of resistance strip 34 in flat engagement with plate 35 but to make doubly sure that this flat'engagement is maintained at all points a sealing medium having high heat conducting characteristics may be interposed therebetween. Under certain circumstances, resistance strip 34 and plate 35" may be bonded to-, gather to form a substantially integral part.

A spring contact member generally indicated at 53 is secured to raised portion l9 (Figure 1) by way of a rivet 59 extending through base Ill and headed over on terminal projection 33. The free end portion ii of contact member 53 engages a suitable contact plate 32 on arm 32; contact plate 32 is electrically connected to armature brush 33. Accordingly, terminal projection 33 is connected to brush 33. A metallic cup-shaped cover member generally indicatedat 33 (Figures 3 and 4).

ly pass through these various parts. When cur- I rent is passing through coating 54 on strip 34, "hot points" may develop in certain portions of the strip. However, such tendency of the resistance material to develop "hot points will immediately result in a withdrawal of the heat from such points and a distribution thereof over the entire length of the resistance strip by way of plate 35. Furthermore, when current is only passing through a portion of coating 54 and thus tending to overheat this portion of strip 34, such heat developed by the pasage of current will be quickly distributed throughout the entire surface of plate 35.

Further still, heat passing from strip 34 or any portion therof to plate 35 will not only be evenly distributed throughout plate 35 but will be rapidly conducted to bushing 21, bottom plate 44 and cover 33. Bushing 21, cover 53 and bottom plate 44 are all exposed to the outside atmosphere and heat transmitted to these parts will be constantly dissipated to cool the entire apparatus.

It will now become clear that plate 35 distributes the heat evenly throughout the resistance strip as it is developed by current passage, thereby avoiding dangerous hot spots along the resistance coating. Also, heat so generated will be rapidly drawn oil. by bushing 21, cover 63 and bottom plate 44 which parts constantly tend to cool the entire apparatus.

It will thus become clear that'I have provided a thoroughly practical power control apparatus in which the several objects hereinabove mentioned as well as many others are successfully accomplished. v

As many possible embodiments may be made of .the above invention and as many changesmight be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth, or shown in the accompanying drawing, is tobe interpreted as illustrative and not in a limiting sense.

I claim:-

1. In apparatus of the class described, in com.- binatioma non-metallic base, a contactor rotatably supported in said base, a metallic plate covering a substantial portion of the top of said base and having portions extending downwardly of said base, a second metallic plate secured to the bottom of said base and engaging said downwardly extending portions of said first plate, a resistance element mounted on said first-mentioned plate and in engagement with said contactor, and a box-like metallic cover member encasing said first plate said contactor and said resistance element, and thermally connected to said bottomplate whereby saidbase is substantially surrounded by thermally connected metallic parts for diffusion of heat;

2. In apparatus of the class described, in combination, a non-metallic base, a contactor rotatably supported in said base, a metallic plate covering -a substantial portion of the top of said base and having downwardly extending ears adjacent the outer side of said base. a second metallic plate disposed on the bottom of said base. said ears of said first plate being bent over said mousse ablysupported in said base, a metallic plate covering ,a substantial portionof the top oi said base and having downwardly extending ears adjacent the outer side of said base, a second metallic plate disposed on the bottom of said base, said downwardly extending ears of said first plate being bent over said second plate to clamp said second plate in position against the bottom of said base, a resistance element mounted on said first-mentioned plate in en agement with said contactor, and a box-like metallic cover member encasing said first plate said contactor and said resistance element, and having a plurality of ears extending downwardly adjacent the outer side of said base and over said second plate in thermal connection therewith to hold said cover member in position, whereby said base is substantially surrounded by thermally connected metallic parts" for diffusion of heat.

4. In apparatus of the class described, in combination, a non-metallic base, a contactor rotatably supported in said base, a metallic plate covering a substantial portion of the top ofsaid base and having downwardly extending ears adlacent the outer side of said base, a second metallic plate disposed on the bottom of said base,

said downwardly extending ears of said first plate being bent over said'second plate to clamp said second plate in position against the bottom of said base, a resistance element mounted on said first-mentioned .plate in engagement with said contactor, anda box-like metallic cover 3 member encasing said first plate said contactor v and said resistance element, and having a" plurality or ears extending downwardly adjacent the outer side or said base and over said second plate in thermal connection therewith to hold said cover member in position, said ears otsaid cover member and said first mentioned plate being in registry and in engagement, whereby said base is substantially surrounded by thermally connected metallic parts for diffusion of heat. 5. In apparatus of the class described, in combination, a non-metallic base, a contactor rotatably supported on said base, a metallic plate covering a substantial portion of the top oi said base and having'downwardly extending ears ad jacent the outer side of said base, a second metallic plate on the bottom of said base, said ears being bent inwardly and engaging said bottom plate to hold both of said plates in position and establish a thermal connection therebetween,

and a resistance element mounted on said first- I mentioned plate in engagement with said contactor, whereby said plates form a large metallic surface thermally connected to said resistance element to rapidly dissipate thereby to the atmosphere.

6. In apparatus of the class described, in comheat generated bination, a non-metallic base, a metallic bushing mounted on said base, a contactor rotatably supported by said'bushing, a metallic plate covering a substantial portion of the top of said base and having portions extending downwardly of said base on the inner and outer sidesthereof, said' inner portions engaging said bushing, a second metallic plate secured to the bottom of said base and engaging some of said downwardly extending portions of said first plate and also engaging said bushing, and a resistance element mounted on said first-mentioned plate in engagement with said contactor whereby said plates andsaid bushing form a large metallic surface thermally connected to saidresistance element to rapidly dissipate, heat' generated thereby to the atmosphere.

.mssn mas'ran. 

